I've just installed to test 3.0 beta 2 and everything seems to work good but when I want to see a post e.g.http://www.pivari.com/video/giudice-di-pace-online-lo-stato-del-procedimento/
I can see correctly the page but the error is
Warning: in_array() [function.in-array]: Wrong datatype for first argument in /usr/local/share/doc/vhost/pivari.com/httpdocs/wp-includes/canonical.php on line 180

I've ran into exactly the same problem. Weird thing was, I'm running 3.0 on two different sites and I see it on one, but not the other. Then I realized that my server was setup to use PHP 4 on one domain and PHP 5 on the other. It was the site running 4 that had the error message. I switched it to 5 and the message went away.